The Study On Structural Styles And Dynamic Mechanism Of Wuerxun Sag In Hailer Basin

Hailar Basin is a meso-cenozoic of multicycle, composite-style, fault-sag basin. It is the focus of the Daqing oil field in the peripheral basin exploration by its special tectonic location, strong post-stage rebuilding, Multi-stage reservoir forming and the accumulation of oil and gas. Wuerxun sag is where Hailar Basin especially explores.The study which is based on previous research, comprehensive analysis and collation of the existing geology, drilling and seismic data, established the stratigraphic frameworks in Wuerxun sag with the theory of structural geology and seismic stratigraphy.The paper exactly analyzes structural styles of Wuerxun sag by the structural theories, such as extensional structure,compressional structure,inverted structure,shear-tensile structure,and gravity structure;and discusses the dynamics mechanism of Wuerxun sag based on the regional geodynamics.The research on the relationship between structural styles and oil provides an important theoretical basis for the next exploration. Through the thesis research, the main access to the following understanding:(1)There are two types of sequence stratigraphic boundary:one is tectonic interface(T04,T3,T31,T4 and T5 seismic reflection layers),the other is depositional interface(T2,T21 and T22 seismic reflection layers).(2)The big fault of fault basin period in the west which is the main fault controlling the Wuerxun sag,is not a north-south fault,but are formed by some northeast faults distributing in echelon form;The sag is controlling by NS direction faults in the period transformed from fault depression to sag .The sag experienced 3 stages big ruptural deformations:the end of sediments in Tongbomiao,the faults,direction is in NE and NW ,and tensile-shear structural deform characteristics;the end of sediments in Yiminzu, the faults are big ,NS,NE and NW directions,cutting across thick stratum;the end of sediments in Qingyuangang,it is compressive and shear ruptural deformation(3)Since Cretaceous Period, Wuerxun sag undertook 4 stages of tectonic movement: Fault depression stage, the period transformed from fault depression to sag Down-warping stage and inversion stage.The structural styles are including most of fault basin structural styles such as normal fault,the combination of normal fault and normal fault-related fold. At the same time there are also many similar the negative flower shaped structure and compression reversed structure style。According to the seismic data interpretation and the law of structure combination analysis , It is verified that the main structure style of Wuerxun sag included five kinds, such as extension, compression, inversion and shear structure and gravity tectonics , in which the extension structure was the principle part. Most of their trends are approximate south-north with zonal distribution in the plane.(4)The Wuerxun sag experienced three times tectonic inversions:the end of sediments in Tongbomiao,the end of sediments in Yiminzu and the end of sediments in Qingyuangang,(5)According to the study about the regional geological setting and evolution of the sedimentaiy basins of Northeast Asia, in marginal-Pacific tectonic domain,the main regional geological background of northeast Asia continent is that Kula plate and Pacific Plate subducted Eurasian Plate,with which geologic events of northeast Asia continental margin have something to do .The basins here distribute in NE,NNE,extending north～south and becoming younger and younger eastward.and southward. The reason is that Westward, subduction angle of the Kula-Pacific plates changed from 10°to 80°during the period,the eastward Moving Hotspots resulted in lithosphere uprising and tension, leading to development of the extensional basins which are younger and younger eastward.The faults controlling the Wuerxunsag of Hailaer basin distributed in NE,NNE directions in fault depression stage,and the ones are approximate south-north in the period transformed from fault depression to sag Down-warping stage and inversion stage. Because of uni-directional ring current of asthenosphere caused by Kula plate subducted in NW,NWW directions and the diapir action of magma from the mantle. lower crust stretched and became thiner by the shearing action of ring current; and the upper crust were brittle fracture to be fault baisn. Pacific plate dived in W-NWW directions fromeEarly Cretaceous (6) There is a close relationship between the oil migration,the location where oil exists and features of faul tand Structural styles.The faults controlposses oil migration by the the pathway characteristics in the initial stage of its forming and sealing ability. Wuerxun Sag had rich oil and gas, complex geologic framework caused the multiple trap types.Reservoir types are mainly faulted nose,faulted anticline,graben or horst and transform structures.That is important and meaningful to oil exploration.